Comparison of Wetland Impact Assessment Methodologies: Charleston Method SOP versus Regional Hydrogeomorphic Models

Best professional judgment has been used historically during the Section 404 permitting process for assessing impacts and required mitigation for wetlands on a per acre basis. In Arkansas, the U. S. Army Corps of Engineers Districts with regulatory responsibility currently utilize the Charleston Method Standard Operating Procedure (SOP), a rapid assessment methodology for determining wetland impact to mitigation ratios. During the past 15 years, the Arkansas Multi-agency Wetland Planning Team (MAWPT) has developed the Hydrogeomorphic Model (HGM), a true functional assessment methodology. The objectives of this study were to compare and contrast wetland impacts and wetland mitigation ratios utilizing the Charleston Method SOP and the HGM to determine which methodology is preferable in terms of effort to perform the analyses and effectiveness in achieving successful wetland mitigation. Two new location highway projects were compared, I-69 Segment of Independent Utility (SIU) 13, a 177-kilometer (110-mile) long segment that crosses the Ouachita River and Saline River floodplain wetlands, and the 7.9-kilometer (4.9-mile) long White River Bridge & Approaches (Clarendon) on U. S. Highway 79. The advantage of the HGM is that the models are calibrated to reference wetlands in the geographic area that are used to assess wetland functions. The HGM requires more time than the Charleston Method SOP, since the latter does not require the collection of any quantitative data. Based on this study of two linear highway construction projects, the Charleston Method SOP requires more mitigation than required to compensate for loss of wetland functions. For the 4-lane divided, new location, 9.0-kilometer (5.6-mile) long I-69 SIU 13 selected alignment crossing of the Ouachita River floodplain, Charleston Method SOP calculations require approximately 1.75 times more mitigation acres than the HGM calculations at an additional cost of $1.48M. For the 2-lane, new location, 7.9-kilometer (4.9-mile) long U.S. Highway 79 crossing of the White River floodplain, Charleston Method SOP calculations require approximately 3.6 times more mitigation acres than the HGM calculations at an additional cost of approximately $607,000. Results from this study suggest that the HGM, in addition to providing science based, data driven evaluation of wetland impacts and mitigation requirements to replace wetland functions, is more cost effective than the Charleston Method SOP despite the additional time and effort required for its utilization.

• Record URL:
  • https://www.ardot.gov/wp-content/uploads/2020/11/TRC0704_Comparison_of_Wetland_Impact_Assessment_Methodologies_Charleston_Method_SOP_versus_Regional_Hydrogeomorphic_Models.pdf
• 
• Corporate Authors:

  Arkansas State Highway and Transportation Department

  Little Rock, AR  United States  72203
• Authors:
  • Langston, Henry W
• Publication Date: 2010-6

Language

• English

Media Info

• Media Type: Digital/other
• Edition: Final Report
• Features: Figures; Maps; Photos; References; Tables;
• Pagination: 38p

Subject/Index Terms

• TRT Terms: Construction projects; Cost effectiveness; Environmental impact analysis; Geomorphology; Hydrogeology; Methodology; Wetlands
• Geographic Terms: Arkansas
• Subject Areas: Environment; Highways; I15: Environment;

Filing Info

• Accession Number: 01548662
• Record Type: Publication
• Report/Paper Numbers: TRC-0704
• Files: TRIS, ATRI, STATEDOT
• Created Date: Dec 23 2014 12:08PM